1. Field of the Invention
The present invention relates to a circuit arrangement for the operation of a fluorescent lamp which is connectable to an alternating-current power supply, for example, the electrical power supply on board an aircraft, including a switch which is located between the lamp electrodes, and which is actuatable through the intermediary of a control circuit whereby the lamp electrodes are heated when the switch is closed.
2. Discussion of the Prior Art
A circuit arrangement of the type mentioned hereinabove is described in German Laid-Open Patent Appln. 33 27 189 A1. The control circuit serves for a dimming of the brightness. Through the opening of the switch, the control circuit generates phase-shifted ignition voltage pulses during each half-wave of the power supply. In the presence of a closed switch, a heating current flows across the lamp electrodes. The ignition voltage pulses are immediately generated during each half-wave of the power supply upon the opening of a power supply switch. Ignition voltage pulses consequently are produced even when the lamp electrodes are not yet adequately preheated.
It has been evidenced that the duration of the working order of a fluorescent lamp and in the life expectancy thereof will be significantly shortened, when attempts at ignition are carried out while the lamp electrodes are still cold. In the circuit arrangement pursuant to German OS 33 27 189 A1 there are produced numerous ignition pulses with lamp electrodes which are still not adequately heated, so that there must only be expected a short life expectancy for the fluorescent lamp.
In the disclosure of Swiss Patent 595,036 there is similarly described a circuit arrangement of the above-mentioned type. In this publication there is mentioned that in the dark control of the fluorescent lamps, through the preheating of the lamp electrodes subsequent to the switching on of the fluorescent lamps, there is avoided a cold-start. However, the manner in which this dark control is implemented is not disclosed.